As for a wake-up system which promotes wake-up of a sleeper by irradiating a wake-up light, a wake-up system that increases output (power, brightness or luminance) of a wake-up light gradually toward a wake-up time, and thereby, awakes a sleeper at the wake-up time is conventionally known (see, for example, JP Hei 7-318670 A, JP 2007-003499 A, or Noguchi Hiroki et al. “Improvement of Wake-up by Irradiation of Gradually Increased Light Before Wake-up Using A Ceiling Illumination”, Journal of the Illuminating Engineering Institute of Japan, 2001, 85 (5), pp. 315-322). In such a wake-up system, when an incandescent lamp is used as a light source, for example, color temperature of the wake-up light is higher in a state that the output of the wake-up light is smaller, and the color temperature of the wake-up light is lower in a state that the output of the wake-up light is larger.
Generally, in a low illumination state where output of light from a light source is smaller, a person feels comfortable when color temperature of the light source is lower, but the person feels uncomfortable when the color temperature of the light source is higher. Alternatively, in a high illumination state where the output of light from the light source is larger, the person feels comfortable when color temperature of the light source is higher but the person feels uncomfortable when color temperature of the light source is lower. (see Kruithof, A. A., “Tubular luminescence lamps for general illumination,” Philips Technical Review, 1941, 6, pp. 65-96). Therefore, in the wake-up system, if the color temperature of the light source is higher when the output of the wake-up light is smaller or the color temperature of the light source is lower when the output of the wake-up light is larger, as mentioned above, there is a fear that the sleeper feels uncomfortable at any time when he/she awakes.